1. Field of the Invention
This invention relates to a facsimile apparatus having an automatic answering telephone function, in which the apparatus has an automatic answering telephone connected thereto and is capable of changing over automatically between the facsimile mode and the automatic answering telephone. The invention further relates to a communication method in this apparatus.
2. Description of the Prior Art
An example of a conventional facsimile communication apparatus to which an automatic answering telephone set is connected is one having an automatic changeover function (TEL/FAX automatic changeover function) for changing over between a telephone mode and a facsimile mode automatically. An NCU (network control unit) in an apparatus of this kind is constructed as shown in FIG. 6. In FIG. 6, terminals L1 and L2 are connected to a line N. An automatic answering telephone 16 is connected to terminals T1 and T2. The automatic answering telephone 16 automatically answers a call signal from the line N. If the calling party is a human being, a voice message from this party is recorded. When the calling party is a facsimile machine, a CNG signal sent by the facsimile machine of the calling party enters a CNG detector 7 through a capacitor 5 and a transformer 6. The CNG detector 7 outputs a CNG detection signal (CNGDET) when it detects the CNG signal. When the CNGDET signal is outputted, the control unit performs automatic communication by changing over a CML relay 1 from the side of T1, T2 to the side of a modem. Thus, when the CNG signal is detected on the line after the automatic answering telephone has answered automatically, the CML relay 1 is changed over, thereby realizing automatic changeover between the automatic answering telephone and the facsimile mode.
More specifically, when there is an incoming call from the line in a state in which the automatic answering telephone has been set to the automatic answering mode in the facsimile communication apparatus of this type, first the automatic answering telephone is started and the line is connected to the side of the automatic answering telephone to playback a pre-recorded answer message (an outgoing message, also referred to as an "OGM") and send this message to the calling side. In parallel with this operation, the signal received from the line is monitored. When the CNG signal (1100 Hz) is detected, as mentioned above, it is determined that the calling side is a facsimile machine and the line is changed over from the side of the automatic answering telephone to the modem side of the facsimile communication apparatus, after which facsimile communication is carried out.
The aforementioned detection of the CNG signal is performed by using a band-pass filter to extract a frequency component of 1100 Hz from the signal inputted by the line.
A problem is encountered in the prior art described above. Specifically, since the operation for sending the answer message is performed in parallel with the detection of the CNG signal and the level of the answer message is higher than the level of the CNG signal, detection of the CNG signal by the above-mentioned band-pass filter is hindered and the TEL/FAX automatic changeover function can operate erroneously.
In order to prevent this erroneous operation, an expedient is to set a fixed silent period, which is for the purpose of preventing collision with the CNG signal, when the answer message is recorded. However, the setting operation is a troublesome one.
Furthermore, in order to change over the CML relay 1 after the CNG signal is confirmed, as mentioned above, the CNG signal is recorded more than one time in the automatic answering telephone. Alternatively, since detection of the CNG signal cannot be performed well during transmission of the answer message, as set forth above, there are cases where the operation of the telephone mode proceeds and the operation for recording the message from the calling party by the automatic answering telephone is initiated. In such case, the CNG signal sent in continuous fashion will be recorded in the automatic answering telephone in the area thereof that is for recording the message from the calling party. If the CNG signal happens to be recorded in this manner and the owner of the facsimile communication apparatus attempts to listen to the recorded contents of a message from a calling party as by a remote control operation from an outside telephone using DTMF or the like, the message when played back will contain the CNG signal. Owing to the CNG signal played back in this manner, the TEL/FAX automatic changeover function will operate erroneously and the apparatus will be changed over to the facsimile mode.